For health and safety reasons, there is a need in medical and dental applications to regularly sterilize equipment, particularly before the equipment is next used on a patient or in a procedure. Improperly sterilized instruments utilized in patient care can result in infection, e.g., at a surgical site, and pose a serious threat to the patient's safety that can lead to life-threatening infection or even death. There is also a need in other industries, such as food/beverage and agricultural industries, for regular sterilization of equipment.
In medical and dental applications, controlling infections is an important concern. Equipment contamination by blood or saliva can easily occur. For example, small, sharp instruments can become contaminated with blood or other fluids, providing ample opportunity for transmission of hepatitis B, hepatitis C and human immunodeficiency virus (HIV). Dentistry potentially exposes much of the population to blood contact with infected patients. Thus, the use of dental equipment may pose an unacceptable risk of cross infection.
In dentistry, re-sterilization of used instruments for reuse on another patient has been a common practice. Although, single-use devices have been promoted as a strategy to prevent cross-infection among patients, re-sterilization of previously used instruments still continues to be a common practice because the cost of single-use devices can be significant.
The American Dental Association Guidelines emphasize the importance of dental instrument sterilization, e.g., “All critical and semi critical dental instruments that are heat stable should be sterilized after each use by steam under pressure (autoclaving), dry heat, or chemical vapor . . . . Sterilization is recommended for all high-speed dental handpieces, low-speed handpiece components used intraorally and reusable prophylaxis angles. It is important to follow the manufacturers' instructions for cleaning, lubrication and sterilization procedures to ensure the effectiveness of the sterilization process and the longevity of these instruments. High-speed and low-speed handpieces produced today are heat tolerant, and many older heat sensitive models can be retrofitted with heat-stable components.”
The term “disinfection” is understood to be a process that kills only vegetative organisms, whereas, “sterilization” kills spores and other microorganisms as well. Under current practices, sterilizing equipment is a time-consuming process that requires careful attention. If strict protocols are not followed, the equipment may become contaminated. For example, in an autoclave sterilization cycle, interruption of the cycle results in inadequately sterilized instruments that cannot be considered safe. After the sterilization cycle, the sterilizer must depressurize, and the packs remain in the sterilizer for drying. The drying phase may take an additional 20-45 min. The unit must only be opened after completion of the drying cycle making it more time consuming in field settings.
Heat sterilization methods are generally preferred to chemical disinfection. However, with certain instruments that are repeatedly used, frequent chemical disinfection may be necessary since heat sterilization can lead to corrosion. Further, it is often not possible to carry out heat sterilization due to time constraints and the need for access to autoclave equipment.
In these situations, disinfection using chemical disinfectants may be considered an alternate for heat sterilization to reduce the risk of cross contaminations. Glutaraldehyde is a dialdehyde that displays potent bactericidal, fungicidal, mycobactericidal, sporicidal and virucidal activities. The mechanism of its action is based on its interaction with amino groups in proteins and enzymes. Glutaraldehyde is normally used as a 2% solution, which is sufficient to achieve a sporicidal effect. It is used as an immersion solution for metallic instruments, face masks, heat sensitive plastic rubbers, and fiber optics.
Hydrogen peroxide (H2O2) is also used for disinfection, sterilization, and antisepsis and is effective against bacteria, viruses, yeast and spores. It is commercially available in concentrations ranging from 3% to 90%. H2O2 is environmental friendly, because it can rapidly degrade into harmless products—water and oxygen. H2O2 acts as an oxidant by producing hydroxyl free radicals (.OH), which attack cell components, including lipids, proteins, and DNA. A proposed mechanism of action is based on its ability to target exposed sulfhydryl groups and double bonds.
Alcohol is an effective skin antiseptic and disinfectant for medical instruments. A number of alcohols have shown effective antimicrobial activity but, ethyl alcohol, isopropyl alcohol and n-propanol are the most widely used. Alcohols exhibit rapid broad-spectrum antimicrobial activity against vegetative bacteria (including mycobacteria), fungi, and viruses but they lack sporicidal activity hence are not recommended for sterilization. In general, the antimicrobial activity of alcohols is optimum in the range of 60-90%, but it becomes significantly lower at concentrations below 50%. The exact mode of action of alcohols is unclear, but it is generally believed that they cause membrane damage leading to cell lysis and result into a rapid denaturation of proteins.